Variable Dilation Angle Models in Rocks, a Review

This paper presents a comprehensive review of dilation angle models in rock mechanics. Dilation, a characteristic behavior of geomaterials, such as rocks and rock masses, involves volumetric changes during plastic deformation. This study focuses on the dilation angle, a key parameter for measuring dilation, and its dependence on the plastic strain history and confining stress. The review covers ten variable dilation angle models developed over the past two decades and analyzes their equations, parameters, and main features. These models range from simple approaches with few parameters to complex formulations that involve multiple coefficients. The strengths and limitations of each model, including their applicability to different rock types and testing conditions, are presented. Key findings include the importance of considering both plastic strain history and confining stress in dilatancy models, the variation in approaches for defining the onset of plastic strain, and the challenges in standardizing and comparing different models. This review also highlights the ongoing debate regarding the influence of rock type, specimen size, and structure on dilatant behavior. This review contributes to the field of rock mechanics by providing a comprehensive overview of the current dilatancy models, their applications, and limitations. It serves as a valuable resource for researchers and practitioners in geomechanical engineering, particularly in areas such as tunnel design, mining engineering, and petroleum extraction, where understanding the post-peak behavior of rocks may be crucial.